Wetting and wettability involve the contact between a liquid and a solid surface, resulting from the intermolecular interactions when the two are brought together. The amount of wetting depends on the energies (or surface tensions) of the interfaces involved such that the total energy is minimized. One measurement of the degree of wetting is the contact angle, the angle at which the liquid-vapor interface meets the solid-liquid interface. If the wetting is very favorable, the contact angle will be low, and the fluid will spread to cover or “wet” a larger area of the surface. If the wetting is unfavorable, the contact angle will be high, and the fluid will form a compact, self-contained droplet on the surface. If the contact angle of water on a surface is low, the surface may be said to be “water-wetted” or “water-wettable”, whereas if the contact angle of an oil droplet on a surface is low, the surface may be said to be “oil-wetted” or “oil-wettable”.
Drilling fluids used in the drilling of subterranean oil and gas wells along with other drilling fluid applications and drilling procedures are known. In rotary drilling there are a variety of functions and characteristics that are expected of drilling fluids, also known as drilling muds, or simply “muds”.
Drilling fluids are typically classified according to their base fluid. In water-based muds, solid particles are suspended in water or brine. Oil can be emulsified in the water which is the continuous phase. Brine-based drilling fluids, of course are a water-based mud (WBM) in which the aqueous component is brine. Oil-based muds (OBM) are the opposite or inverse. Solid particles are often suspended in oil, and water or brine is emulsified in the oil and therefore the oil is the continuous phase. Oil-based muds can be either all-oil based or water-in-oil macroemulsions, which are also called invert emulsions. In oil-based mud the oil can consist of any oil that may include, but is not limited to, diesel, mineral oil, esters, or alpha-olefins. OBMs as defined herein also include synthetic-based fluids or muds (SBMs) which are synthetically produced rather than refined from naturally-occurring materials. SBMs often include, but are not necessarily limited to, olefin oligomers of ethylene, esters made from vegetable fatty acids and alcohols, ethers and polyethers made from alcohols and polyalcohols, paraffinic, or aromatic hydrocarbons, alkyl benzenes, terpenes and other natural products and mixtures of these types.
When OBMs and/or SBMs (sometimes collectively referred to as non-aqueous fluids or NAFs) are used, the subterranean rock formations become oil wet and resistant to treatments using pills that are water-based. In the oilfield, a pill is any relatively small quantity (e.g. about 200 barrels or less (32 kiloliters)) of a special blend of a drilling fluid used to accomplish a particular task or job that a regular drilling fluid cannot perform. Non-limiting examples include high-viscosity pills to help lift cuttings out of a vertical wellbore; freshwater pills to dissolve encroaching salt formations; pills to free stuck pipe, such as to relieve differential sticking forces or to destroy filter cake; lost circulation or fluid loss pills to plug a thief zone or inhibit fluid from being lost into a relatively high permeability zone; and crosslink pills to deliver and crosslink polysaccharides such as guar gums to increase viscosity in a certain zone to prevent or inhibit fluid loss.
It would be desirable if compositions and methods could be devised to aid and improve the ability to switch or convert the wettability of a rock formation that is oil-wet into a water-wettable rock so that subsequently introduced water-based pills would perform and/or be more effective.